Starring Kathryn Newton

At a public school in Monterey, a murder suddenly occurs on trivia night, but neither the victim nor the murderer is revealed. Backtracking to the first day of school, the families of five first-graders are introduced. Madeline Martha Mackenzie is a strong-willed, wealthy, and feared alpha female in town with a first-grade daughter and teenage daughter from an earlier marriage. Her friend, a retired lawyer Celeste Wright, is the mother of twin sons who are also beginning at that same school. New to town is Jane Chapman – a young single mother raising her son, Ziggy. Renata Klein’s daughter Amabella accuses Ziggy of attempting to choke her, which he denies. Madeline and Celeste befriend Jane. Secrets are revealed, including that Madeline is struggling to cope with her ex-husband Nathan’s marriage to a yoga instructor named Bonnie and also trying to build a relationship with her older daughter. Celeste appears to have a very happy life with her husband Perry, but he starts to show signs of being violent. Jane’s motives for moving to Monterey are unknown.

Perry lashes out at Celeste when he discovers he missed orientation at the school, but Celeste lets it slide. Jane looks for work with little success. Madeline goes on the warpath with Renata when it is revealed Renata did not invite Ziggy to Amabella’s birthday party. Ed questions Madeline’s devotion to him when she continues to complain about seeing Nathan with Bonnie all the time. Madeline is further disturbed when Bonnie takes her oldest daughter, Abby, to Planned Parenthood. Nathan tries to come to a peaceful resolution with Ed about their parenting of Abby, but Ed senses Nathan trying to intimidate him and stands firm. Madeline’s younger daughter, Chloe, and Bonnie’s daughter, Skye, attempt to mend the wounds between Ziggy and Amabella but it leads to an incident of unwanted affection and the parents of the four children are called into the principal’s office, leading Jane to have a flashback of an unwanted episode.

Perry chokes Celeste when he believes she deliberately left him out of a family gathering, after which Celeste threatens to leave him. Renata’s party for Amabella is a huge success but she is ultimately upset when Madeline invited Amabella’s closest friends and Ziggy to Disney on Ice on the same day. At therapy, Perry claims his outbursts are out of fear that Celeste does not love him, which Celeste attempts to deny. When Abby’s academic performance begins to decline her guidance counselor suggests it is being caused by stress at home so Abby decides to live with Nathan, much to Madeline’s dismay. Jane gets Ziggy involved with more extracurricular activities and helps him construct a family tree for school with Madeline’s help. Jane lashes out at Ziggy when he insists on putting his father’s name on the tree, and Jane confides to Madeline that Ziggy was the result of rape by a man named Saxon Banks, whom she has not seen since.

Abigail moves in with Nathan and Bonnie. Celeste legally represents Joseph and Madeline in a meeting with the Mayor regarding the controversial Avenue Q, and successfully convinces the Mayor to allow the play to proceed. In the process, she realizes her desire to return to work. She asks her therapist how to best convince Perry but Dr. Reisman is more concerned with why Celeste is afraid to do so. At home, Perry tells Celeste not to attend any future meetings. When she refuses, he grabs her by the throat but quickly relinquishes when one of their boys enters the room. Joseph and Madeline kiss and it is revealed they had an affair a year ago. Madeline locates a man online named Saxon Baker whom she believes to be Saxon Banks. She informs Jane and Celeste, and they plan to travel to San Luis Obispo to confront him. Ms. Barnes, the teacher, suspects Amabella is still being bullied. Despite Amabella’s assertions that she and Ziggy are friends, Ms. Barnes requests Jane to have Ziggy psychologically evaluated. The psychologist believes that Ziggy is innocent and that he may actually be being bullied himself.

Nathan spots Jane at the gun range and tells Madeline. Although Jane reassures Madeline that she carries a gun solely for its psychological benefits, Madeline begins to regret tracking down Saxon Baker. Renata discovers a bite mark on Amabella’s arm, but Amabella refuses to disclose who bit her. Renata assumes it is Ziggy and a meeting is held between Jane and the school principal. Joseph is convinced Madeline still has feelings for him but she maintains that their affair is over. While they argue, their car crashes. Madeline is uninjured, while Joseph is hospitalized. The incident raises suspicion from Ed and Joseph’s wife, Tori. Perry is angered when Celeste does not ask the twins to tidy their toys. A confrontation triggers further violence from Perry, followed by aggressive sex. Later, Dr. Reisman confronts Celeste with the belief that Celeste is being abused; Celeste eventually reveals that she has previously feared for her life and had considered leaving Perry. Dr. Reisman urges Celeste to leave him. Jane secretly travels to San Luis Obispo to confront Saxon Baker, taking her gun with her.

Jane reveals to Madeline that she went to confront Saxon Baker, who turns out to be the wrong man. Madeline attempts to convince Jane to give up the search. Ms. Barnes relays to Jane that a petition has begun to have Ziggy suspended. Jane confronts Renata and mistakenly gouges her eye. Jane apologizes, realizing that they both want to protect their children. Renata forgives Jane and reveals her plan to schedule play-dates with each of Amabella’s classmates to discover who is hurting her. Celeste’s therapist advises her to prepare to leave Perry by renting an apartment and disclosing the abuse to friends. Later, Perry tries to initiate sex with Celeste, who defensively fractures his penis. Returning from the hospital, Perry tells Celeste she is “lucky” he did not kill her. The following day she begins looking for an apartment. At the opening night of Avenue Q, Tori confronts Madeline about having an affair with Joseph. At home, Madeline and Ed have another argument about her lack of passion toward him, which culminates in her alluding to having made a “terrible mistake”. Nathan discovers that Abigail’s “secret project” is auctioning her virginity to raise money for Amnesty International. Madeline furiously confronts Abigail, disclosing her affair in the process.

Following another beating, Celeste decides to leave Perry the day after trivia night. Ziggy confesses to Jane that it was Max who choked Amabella. Madeline talks to Joseph about his wife knowing about their affair. Jane tells Celeste that her son Max is the bully. When preparing to leave for trivia night, Perry sees a text message on Celeste’s phone from the landlady of her new apartment. He confronts her on the way to the party, but is interrupted by Renata. At the party, Celeste tells Renata that Max is the bully. Meanwhile, a drunk Madeline runs away during Ed’s singing performance. Jane goes after her and finds her atop stairs at the back of the venue. Madeline tells Jane that she cheated on Ed. Renata also goes after them and apologizes to Jane for having blamed Ziggy. Celeste joins the women, followed by Perry. Bonnie follows them and watches the group from afar. Jane sees Perry and realizes that he is the rapist. Perry pleads with Celeste to come back home with him and when she declines, he viciously attacks her. The group unsuccessfully fights Perry off until Bonnie rushes in and pushes him down the stairs, killing him. In police interviews, the women confirm that there was a fight with Perry but claim he fell accidentally. Despite Detective Quinlan’s skepticism, the police accept their version. Later, the five women and their children lounge at the beach, where Detective Quinlan continues to watch them.